1. Field of the Invention
The invention is related to the field of communication networks and, in particular, to performing online charging in a proxy online charging system (OCS) of a visited network that is serving roaming users.
2. Statement of the Problem
Service providers typically provide numerous voice and/or data services to subscribers using one or more wireline and/or wireless communication networks. Exemplary services include cellular telephony, access to the Internet, gaming, broadcasting or multicasting of audio, video, and multimedia programming, etc. Mobile devices, such as cell phones, personal data assistants, smart phones, pagers, text messaging devices, global positioning system (GPS) devices, network interface cards, notebook computers, and desktop computers, may access the services provided by the communication networks over an air interface with one or more base stations. Communication between the mobile devices and base stations are governed by various standards and/or protocols, such as the standards and protocols defined by the 3rd Generation Partnership Project (3GPP, 3GPP2).
The service providers use offline and online billing functions to keep track of the charges incurred by each device for using the various services. The 3GPP/3GPP2 standards groups have defined a set of specifications that may be used to implement online charging systems and offline charging systems to cover charging in the various network domains (e.g., a circuit switching network domain, a packet switching network domain, and/or a wireless domain), IP multimedia subsystems, and emerging 3G/OMA application services.
Online charging is generally defined as a charging mechanism where charging information can affect, in real-time, the service rendered, and therefore a direct interaction of the charging mechanism with session/service control is needed. In online charging, charging information for network resource usage is collected concurrently with the resource usage. However, authorization for the network resource usage must be obtained by the network prior to the actual resource usage. The network elements in a communication network include Charging Trigger Functions (CTF). For online charging, the CTF triggers on charging events, collects charging information pertaining to the charging events, and assembles the charging information into matching charging events. The CTF then transmits credit request messages to the Online Charging System (OCS) to obtain authorization for the charging event/network resource usage requested by the user. The CTF delays the actual resource usage until permission has been granted by the OCS. When a granted quota of service units is obtained from the OCS, the CTF performs budget control during the resource usage. The CTF enforces termination of the end user's resource usage when permission by the OCS is not granted or expires.
Mobile communications allow for a mobile user to roam among networks. Roaming is a general term in mobile communications that refers to the extending of service in a location that is different from the home location where the service was registered. The term “roaming” originates from the GSM world where roaming is defined as the ability for a cellular customer to automatically make and receive voice calls, send and receive data, or access other services when traveling outside the geographical coverage area of the home network by means of using a visited network.
One type of communication network that allows for mobile communications is a cellular network. If a mobile user roams into a visited cellular network, such as a GSM network or a CDMA network, the Mobile Switching Center (MSC) in the visited cellular network serves calls for the roaming user. If a call is placed by the roaming user, the serving MSC collects online charging information for the call, and transmits the online charging information to the home MSC in the home cellular network. The home MSC then interfaces with the prepaid charging system (usually a Service Control Point (SCP)) for real-time credit control for the call.
Another type of communication network that allows for mobile communications is an IP Multimedia Subsystem (IMS) network. Before a communication device receives service from an IMS network, the communication device (commonly referred to as user equipment (UE)) attempts to register with the IMS network. To register according to 3GPP standards, the communication device transmits a register request message, such as a SIP REGISTER message, to a Proxy-Call Session Control Function (P-CSCF) through the appropriate access network. The P-CSCF identifies the home IMS network for the communication device, and then transmits another register request message to a Serving-Call Session Control Function (S-CSCF) in the home IMS network of the user. Responsive to the register request message, the S-CSCF authenticates the user, and provides session control for any session involving the user.
When a mobile user is roaming in the service area of a visited IMS network, the visited IMS network does not provide session control. If a roaming session is initiated, then the P-CSCF in the visited IMS network receives a session initiation message for the session (e.g., SIP INVITE message). The P-CSCF proxies the session control for the session to the S-CSCF in the home IMS network of the mobile user by forwarding the session initiation message to the S-CSCF. The S-CSCF in the home IMS network then provides session control for the session.
While providing session control, the S-CSCF in the home IMS network also provides charging control. The P-CSCF or the S-CSCF in the visited IMS network will route SIP messages to the home S-CSCF responsive to which the home S-CSCF will query the home online charging system (OCS) via Diameter Ro protocol to perform online charging for roaming sessions.
Other types of networks are being developed to provide voice and data communications for mobile users. One present project within the 3GPP is the Long Term Evolution (LTE) which is a project to improve the UMTS mobile phone standard to cope with future requirements. The architecture defined by this project is referred to as the Evolved Packet System (EPS). The EPS architecture comprehends E-UTRAN (Evolved UTRAN) on the access side and EPC (Evolved Packet Core) on the core side.
For a roaming case, the network elements in LTE/EPC networks, such as the serving gateway (SGW), the Packet Data Network gateway (PDN-GW), the HRPD Serving gateway (HSGW), or a AAA proxy server, are located in the visited network. Also, according to existing standards and practices, the OCS is always located in the home network even when the subscriber roams to a visited network. For example, the technical specification 3GPP TS 32.820 describes the online charging architecture for an EPC network. This technical specification describes the OCS always located in the home network.
One problem in LTE/EPC networks is that the network elements in the visited network need to interface with the home OCS to perform online charging for the roaming sessions. Interfacing with the home OCS may be impractical due to signaling security, delay issues, and other issues. Thus, it would be desirable to develop an improved manner of performing online charging for roaming sessions in LTE/EPC networks.